The effect of the sequence of phosphorous and cobalt addition to silica on the activity and product selectivity for Fischer-Tropsch synthesis was investigated using a slurry phase continuously stirred-tank reactor. Advantages of P-modified silica supported cobalt included higher activity and C-5(+) selectivity in comparison with both the undoped and P-doped cobalt silica catalysts. Results of hydrogen chemisorption revealed that cobalt dispersion was higher for all three P-containing cobalt catalysts compared to the undoped cobalt catalyst. H-2-TPR profiles indicate P increases the fraction of high-temperature reducible cobalt oxide species and these surface species were dominant in the case of co-impregnated and P-doped cobalt silica catalysts. P-modified silica had enhanced FT activity likely by altering the surface interactions of cobalt with the hydroxyl groups on silica. (C) 2017 Elsevier B.V. All rights reserved.